The rim of a wire spoke wheel can be misaligned relative to its axle or spindle in two important aspects, and in each case, adjustment is required. Firstly, the wheel rim can be radially or concentrically misaligned and thus be out-of-round, non-circular, or even egg-shaped. Secondly, each side of the wheel rim can have portions thereof disposed at varying distances from a central reference plane normal to the wheel axle and thus the rim can be laterally misaligned or "out-of-true". Where a wheel is laterally misaligned, the rim portions can be displaced laterally to either side of the reference plane thereby causing such a wheel to be "wobbly".
Gross misalignments oftentimes occur when the wheel is first assembled by "lacing" the spokes through the wheel hub and rim. Also, misalignments can occur after a properly assembled wheel is used and thus subjected to road shocks and stresses. Misaligned wheels are undesirable, because an egg-shaped wheel causes a bumpy ride and can collapse, and a wobbly wheel, in addition to giving an unsatisfactory ride, can cause brakes, of the rim-engaging type, to clamp improperly. Therefore, it is desirable to regularly inspect wire spoke wheels and remove all misalignments therefrom by adjusting the tension of the spokes with a conventional spoke wrench. The technique of aligning wire spoke wheels, particularly bicycle wheels, is conventionally referred to as "truing" the wheel.
Spoke wheels have been aligned by mounting them on a stand for rotation about their axes and then by positioning an indicating device or apparatus opposite the wheel rim. Misalignments of the wheel are then checked by the indicating device, while manually rotating the wheel. Proper alignment can then be carried out by adjusting the tension of the spokes.
Many different types and kinds of wheel alignment indicating devices are known in the art. The simplest type of device generally includes a pair of fingers, such as nails, positioned adjacent the opposite sides of, and near to, the rim to detect lateral misalignments thereof. Misalignments are indicated audibly by the sound of the fingers scraping the portions of the rim as the wheel is rotated about its axis and wobbles from side to side. However, such audible indications are oftentimes ambiguous in that a difficult judgment must be made as to which side of the rim caused the scraping sound. Additionally, the mechanical interactions between the fingers and the rim are not very precise and sometimes difficult to detect, thus making it difficult, if not impossible, to obtain an indication of small or minor misalignments.
In a more elaborate prior-known apparatus, at least one stand-mounted dial indicator gauge is used to provide a visual, numerical indication of misalignment. While such an apparatus is highly accurate to use, it is very expensive. Furthermore, if only one gauge is utilized, it can be difficult, if not impossible, to obtain usable readings where the wheel being tested is greatly out-of-true. With such a grossly misaligned wheel, the rim can wobble so far away from engagement with the dial indicator gauge probe during rotation of the wheel, that meaningful indications of out-of-trueness cannot be obtained. Also, with only one gauge, thick or thin portions of the rim due, for example, to welds, are not at all readily detectable, thereby resulting in inaccurate adjustments. Moreover, using only one gauge, it is difficult, if not impossible, to detect simultaneously both out-of-trueness and out-of-roundness. In this regard, in order to detect out-of-roundness, the tire is sometimes removed from the rim and such removal and subsequent replacement is time-consuming and inconvenient.
The use of two or more dial indicator gauges can alleviate the foregoing problems, but this increases correspondingly the complexity and cost of the apparatus. Furthermore, if a pair of spaced-apart dial indicator gauges are mounted on opposite sides of the rim to detect lateral misalignment as the rotating wheel wobbles from side to side, simultaneous readings of both gauges by a single observer is not possible. Thus, the head of the observer must move from one side of the wheel to the other alternatingly as the wheel rotates to determine which side of the rim is deviating too far away from the common transverse plane of reference. Moreover, inaccuracies result from the initial set up of the equipment, in that zero readings for the gauges can only be estimated.
A highly precise and accurate method and apparatus for indicating misalignments in wire spoke wheels is disclosed in U.S. Pat. No. 4,216,942. However, the apparatus employs complex, expensive linkages, and is unable to provide simultaneous indications. Also, complex and time-consuming set-up procedures are required.
In U.S. Pat. No. 4,143,464, there is disclosed a spoke wheel alignment checking apparatus, which checks one side only of the rim. The apparatus disclosed in U.S. Pat. No. 3,951,563 detects radial displacements of a disc wheel using a transducer for producing a continuous analog signal representative of the exact shape of the outer periphery of the wheel, whereby the signal is supplied to a computer for controlling the operation of a central hole borer for the wheel; however, no lateral misalignments are detected.
It would be highly desirable to have a relatively inexpensive apparatus and a convenient to use method for detecting and indicating simultaneously various types of misalignment of a wheel in a highly accurate manner. Such an apparatus and method should provide indications of misalignments in an accurate and unambiguous manner, while distinguishing the type of misalignment present in a given portion of a tire-mounted wheel rim under test. Moreover, misalignment indications should be given for both grossly and only slightly misaligned wheels. Also, such apparatus should be able to be used independently of a stand, and thus could be sold for use with existing stands.